Tilt-frame uav for agricultural air sampling with a propeller-thrust-governing system that facilitates vtol capability

ABSTRACT

We describe an aircraft design, which is capable of vertical takeoff and landing and also high-speed cruise on a fixed wing. The aircraft comprises a fuselage with a probe-deployment mechanism, which deploys a sample-gathering probe, located at a front end of the fuselage. A main wing is coupled to a middle section of the fuselage, wherein a right motor and right propeller are coupled to a right side of the main wing, and a left motor and left propeller are coupled to a left side of the main wing. The right and left propellers are angled with respect to the fuselage enabling the aircraft to pitch up to a vertical-takeoff mode and pitch down a horizontal-cruising mode. A pitch motor and pitch propeller are located at the rear end of the fuselage, wherein the pitch propeller is angled to provide substantially vertical thrust to control a pitch of the fuselage.

RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119 to U.S.Provisional Application No. 62/512,928, entitled “Aerial Vehicle withPropeller-Thrust-Governing System that Provides VTOL Capability andFacilitates Maximum Reach Probe Deployment” by the same inventors as theinstant application, filed on 31 May 2017, the contents of which areincorporated herein by reference.

BACKGROUND Field

The disclosed embodiments generally relate to the design of aerialvehicles with vertical take-off and landing (VTOL) capability, and whichcan also achieve high-speed cruising flight on fixed wings. Morespecifically, the disclosed embodiments relate to an unmanned aerialvehicle (UAV), which is designed for sampling agricultural volatileorganic compounds (VOCs) with a thrust-governing system that facilitatesboth VTOL capability and control of level flight sustained by rigid-winglift.

Related Art

Due to their low operating costs, UAVs are becoming increasingly popularfor agricultural applications. Moreover, UAV avionics are growingsmaller in size and weight while improving performance. This makes iteasier to install high-definition video, infrared-imaging, and thermalcameras onboard UAVs for remote sensing missions. UAVs have beensuccessfully used in agriculture to collect data for NormalizedDifference Vegetation Index (NDVI) computations and to produce thermalimagery for quantifying intra-field vegetation distribution. Lidars arealso becoming readily available in small packages and can be used tocreate three-dimensional maps for forest density studies. (Note that theterms UAS and UAV are used interchangeably throughout this specificationand the appended claims.)

The remote sensing applications for UAVs in agriculture are alreadynumerous and are enjoying sustained growth. The most common UAV sensorsfor agricultural use are cameras, with a variety of spectralcapabilities. Fixed-wing agricultural UAVs are often employed to gatherimagery over larger and/or more-remote fields because of their longrange and endurance. In contrast, multirotor UAVs are appropriate forflight over smaller fields at lower altitudes because of their slowerspeeds, hover capabilities, and limited endurance.

There are additional sensors, which are possible to use for collectingagricultural information in the field. For example, it can beeconomically valuable to be able to collect samples of Volatile OrganicCompounds (VOCs) dispersed in the air to assess the health of specifictypes of crops. However, in order to collect such VOC samples, a UAVmust fly low and slow, or land within the crops. Unlike aerial imagery,VOC collection is not instantaneous—a significant volume of air must besampled to obtain measureable concentrations of VOCs, so flying whilesampling significantly reduces sampling accuracy. Moreover, landingsafely within a producing field or orchard is impossible for a fixedwing UAV and can be only achieved by an aircraft with VTOL capability.Due to the limited endurance and range of multirotor UAVs, landings canonly be conducted across small fields. However, this limited rangedefeats the purpose of using a UAV instead of a handheld device forperforming VOC sampling. Note that it is impractical to uselimited-range multirotors to perform VOC sampling across large fields,because the power source (usually a battery) would have to be changedrepeatedly to a multirotor to traverse the large fields. Therefore,neither traditionally-deigned multirotor UAVs nor fixed-wing UAVs arewell-suited to agricultural VOC sampling demands.

A tiltrotor UAV design can potentially provide a practical alternativeto fixed-wing and multirotor UAV designs for VOC sampling applications.A tiltrotor is a multirotor/fixed-wing hybrid, which is capable of VTOLand relies on wings during a cruising mode. Tiltrotors typically have apropulsion system that turns 90 degrees to switch between horizontal andvertical positions with respect to the aircraft. During take-off, thetiltrotor orients its engines vertically. After gaining altitude, theengines pitch forward to transition to a horizontal position for acruising mode. During this transition, the aircraft picks up speed andtransfers lift from the engines to the wings. During landing, theprocess is reversed. Note that a tiltrotor's VTOL capability allows itto land like a multirotor and save energy while collecting VOCs. Thetiltrotor also provides a cruising range similar to a fixed wingaircraft, which is considerably higher than cruise ranges fortraditional multirotor UAV's.

In theory, these characteristics should enable a tiltrotor toefficiently monitor VOCs in much larger fields. However, this is notalways the case. The tilting mechanism is complex and adds significantweight. Hence, tiltrotors tend to be heavier than size-equivalentmultirotor or fixed-wing aircraft. Moreover, the aerodynamic performanceof tiltrotors is usually worse than fixed-wing aircraft due to variablegeometries.

Hence, what is needed is a new conceptual design for tiltrotor UAVs foragricultural atmospheric sampling applications—one which does not sufferfrom the above-described performance limitations of existing tiltrotorsystems.

SUMMARY

The disclosed embodiments relate to an aircraft design, which is capableof vertical takeoff and landing and also high-speed cruise on a fixedwing. This aircraft includes a fuselage, and a probe-deploymentmechanism located at a front end of the fuselage, wherein theprobe-deployment mechanism is configured to deploy a sample-gatheringprobe. It also includes a main wing coupled to a middle section of thefuselage, wherein a right motor and associated right propeller arecoupled to a right side of the main wing, and a left motor andassociated left propeller are coupled to a left side of the main wing.The right and left propellers are angled with respect to the fuselage toprovide thrust-generation lines, which are similarly angled with respectto the fuselage, which enables the aircraft to pitch up to avertical-takeoff mode and pitch down a horizontal-cruising mode. Theaircraft also includes a pitch motor and associated pitch propellerlocated at the rear end of the fuselage, wherein the pitch propeller isangled to provide substantially vertical thrust to control a pitch ofthe fuselage. When the aircraft is pitched up, the front end of thefuselage sits higher than a rear end of the fuselage to allow theprobe-deployment mechanism to extend higher.

In some embodiments, the probe-deployment mechanism includes anextendable boom, which extends the sample-gathering probe away from theaircraft.

In some embodiments, the sample-gathering probe is configured to samplevolatile organic compounds (VOCs).

In some embodiments, the aircraft further comprises one or more landingsupports, which support the aircraft after a vertical landing so thatthe front end of the fuselage sits higher than the rear end of thefuselage, which facilitates extending the sample-gathering probe aboveand away from the aircraft.

In some embodiments, the one or more landing supports comprise thefollowing three landing supports: a right leg extending from the middlesection of the fuselage; a left leg extending from the middle section ofthe fuselage; and a tail support extending from the rear end of thefuselage.

In some embodiments, the aircraft further comprises: a rightPropeller-Thrust-Governing System (PTGS) located in proximity to theright propeller; and a left PTGS located in proximity to the leftpropeller. During operation of the aircraft, the right and left PTGS sare adjustable to reduce and/or redirect thrust from the associatedright and left propellers.

In some embodiments, by reducing and/or redirecting thrust from the leftand right propellers, the left and right PTGSs control a roll-axisrotation and a yaw-axis rotation for the aircraft.

In some embodiments, each PTGS comprises a pair of adjustable butterflyflaps located in an airflow of an associated propeller.

In some embodiments, each pair of butterfly flaps includes: afront-facing flap, which faces a front of the aircraft; and arear-facing flap, which faces a rear of the aircraft.

In some embodiments, the left motor, the right motor and the pitch motorcomprise a tri-motor system, wherein the left and right motors areprimarily responsible for generating thrust and controlling roll-axisand yaw-axis rotations for the aircraft, and wherein the pitch motor isprimarily responsible for controlling a pitch-axis rotation for theaircraft.

In some embodiments, the right and left propellers are fixedly attachedto the main wing so that the angles of the right and left propellerscannot change with respect to the fuselage.

In some embodiments, the pitch motor comprises a variable-speed motor.

In some embodiments, the aircraft comprises an unmanned aerial vehicle(UAV).

The disclosed embodiments also relate to a propeller-thrust-governingsystem (PTGS) for an associated propeller. This PTGS includes one ormore control surfaces located in an airflow of the associated propeller,wherein the one or more control surfaces are adjustable to reduce athrust produced by the associated propeller, and wherein the one or morecontrol surfaces are also adjustable to redirect the thrust produced bythe associated propeller.

In some embodiments, the PTGS and the associated propeller arecomponents of an aircraft. By reducing and/or redirecting the thrustproduced by the associated propeller, the PTGS facilitates controllingone or more of the following for the aircraft: a roll-axis rotation; ayaw-axis rotation; a pitch-axis rotation for the aircraft; and a levelof propulsion.

In some embodiments, the one or more control surfaces comprise a pair ofadjustable butterfly flaps located in the airflow of the associatedpropeller.

In some embodiments, each flap in the pair of adjustable butterfly flapsis independently controllable.

In some embodiments, the pair of adjustable butterfly flaps includes astandard flap in a standard orientation, wherein a hinged leading edgeof the flap is closer to the associated propeller than a trailing edgeof the flap. It also includes an inverted flap in an invertedorientation, wherein the trailing edge of the flap is closer to theassociated propeller than the hinged leading edge of the flap.

The disclosed embodiments also relate to a system for gathering volatileorganic compound (VOC) samples from a tree in an orchard. Duringoperation, the system vertically lands an unmanned aerial system (UAS),which is capable of vertical take-off and landing (VTOL), in proximityto the tree in the orchard. Next, the system shuts down a propulsionsystem for the UAS, and extends a VOC sensor from the UAS toward acanopy of the tree. The system then collects a VOC sample by activatingthe VOC sensor for a predetermined amount of time. After the sampling iscomplete, the system retracts the VOC sensor back to the UAS andrestarts the propulsion system for the UAS. Finally, the system performsa vertical takeoff with the UAS, and flies the UAS back to a base oranother sampling location.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A presents a perspective view of a tilt-frame unmanned aerialsystem (UAS) in accordance with the disclosed embodiments.

FIG. 1B presents another perspective view of the tilt-frame UAS inaccordance with the disclosed embodiments.

FIG. 2A presents a perspective view of a butterfly flap system inaccordance with the disclosed embodiments.

FIG. 2B presents another perspective view of the butterfly flap systemin accordance with the disclosed embodiments.

FIG. 2C presents a side view of the butterfly flap system in accordancewith the disclosed embodiments.

FIG. 2D presents an exploded view of the butterfly flap system inaccordance with the disclosed embodiments.

FIG. 3 illustrates a tilt-frame UAS, which has landed in proximity to atree, in accordance with the disclosed embodiments.

FIG. 4 presents a flow chart illustrating the process of gathering VOCsamples from a tree in accordance with the disclosed embodiments.

Table I provides a list of agricultural UAS design characteristics inaccordance with the disclosed embodiments.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the present embodiments, and is provided in thecontext of a particular application and its requirements. Variousmodifications to the disclosed embodiments will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to other embodiments and applications without departing fromthe spirit and scope of the present embodiments. Thus, the presentembodiments are not limited to the embodiments shown, but are to beaccorded the widest scope consistent with the principles and featuresdisclosed herein.

The data structures and code described in this detailed description aretypically stored on a computer-readable storage medium, which may be anydevice or medium that can store code and/or data for use by a computersystem. The computer-readable storage medium includes, but is notlimited to, volatile memory, non-volatile memory, magnetic and opticalstorage devices such as disk drives, magnetic tape, CDs (compact discs),DVDs (digital versatile discs or digital video discs), or other mediacapable of storing computer-readable media now known or later developed.

The methods and processes described in the detailed description sectioncan be embodied as code and/or data, which can be stored in acomputer-readable storage medium as described above. When a computersystem reads and executes the code and/or data stored on thecomputer-readable storage medium, the computer system performs themethods and processes embodied as data structures and code and storedwithin the computer-readable storage medium. Furthermore, the methodsand processes described below can be included in hardware modules. Forexample, the hardware modules can include, but are not limited to,application-specific integrated circuit (ASIC) chips, field-programmablegate arrays (FPGAs), and other programmable-logic devices now known orlater developed. When the hardware modules are activated, the hardwaremodules perform the methods and processes included within the hardwaremodules. The methods and processes described in the detailed descriptionsection can be embodied as code and/or data, which can be stored in acomputer-readable storage medium as described above.

Mission

Instead of starting with a generic multirotor platform and tailoring itto an agricultural mission, the agricultural UAS was designed from theground up for a specific agricultural mission. In particular, the UAS isequipped with a VOC sampler capable of collecting and/or analyzing airsamples. During operation, the UAS is designed to land in a citrusorchard between rows of trees and power down its rotors. The UAS thenproceeds to extend a sampling tube, which is mounted on an extendableboom, towards a targeted tree's canopy. See FIG. 3, which illustratesUAS 306, which has landed in proximity to a tree 300 and has deployed aboom 304 with a VOC sampler 302 towards the canopy of tree 300. By usingan air pump, air in vicinity to tree 300 is drawn through the samplingtube for a predetermined amount of time. Once a sample of sufficientvolume is collected, the UAS 306 retracts boom 300 and performs avertical take-off to gain enough altitude to clear the tree canopy. TheUAS 306 then transitions to a horizontal flight mode and cruises to thenext targeted tree. After completing a sequence of targeted stops, theUAS 306 returns to its original point of deployment.

Design Parameters

The design of the agricultural UAS is mission driven. This mission canbe defined as the delivery of a sensor to an orchard for VOC sampling.The weight and size of the payload dictates the weight and size of theUAS. The payload size has not been precisely established, but a roughestimate for the payload mass (0.3 kg) was used as a starting point.Knowing this payload mass, a rough estimate for the expected aircraftweight can be calculated using acceptable load fractions. For apropeller-driven VTOL aircraft, the load fraction is commonly between25%-35% of the aircraft weight. (See M. Gatti and F. Giulietti,“Preliminary design analysis methodology for electric multirotor,” IFAC,2013.) Given that the design calls for a long range/endurance aircraftwith a lithium-ion battery power source, this load fraction should bereduced because of the relatively low energy density of batteries. Aload fraction of 10%-15% was chosen because it is better suited forcompleting a mission with the desired range/endurance characteristics.

With the given load fraction, the estimated UAS mass is calculated to bebetween 3 kg and 2 kg. To achieve VTOL, the thrust generated by themotors must be capable of exceeding the weight of the aircraft. Thus,the motors collectively must be capable of producing 20 to 30 Newtons ofthrust. Note that the thrust generated by the motors is dependent onmany factors. Hence, thrust alone cannot be used to size motors. Motorsare typically sized based on the amount of power they are able to safelyhandle. Most electric, battery-powered multirotors have a minimum powerto weight ratio of □165 W/kg for hovering operations. (See D. Bershadskyand S. Haviland, “Electric multirotor propulsion system sizing forperformance prediction and design optimization,” AIAA SciTech Forum,2016.) Using this estimated value, the power required for theagricultural UAS is between 330 watts and 500 watts for take-off andlanding operations.

The design for the agricultural UAS is based on a tri-copter platform,and the total required thrust is shared between three motors. Note thatthe rear motor is primarily used for stabilization. Therefore, itscontribution to thrust can be considered negligible for initialestimates. The power load is thus mainly shared between the front twomotors of the UAS. From these power estimates, the load on each mainmotor will not exceed 250 watts during hovering operations. However, inorder to keep motor temperatures low and have a considerable factor ofsafety, a larger main motor was selected. The selected main motors wererated at 700 W each providing a safety factor of □2.8. The rear motor isprimarily responsible pitch control and therefore a smaller motor of 286W was chosen.

In addition to sizing the motors, power estimates during hoveroperations are used to size the UAS flight battery. Typical maximumflight endurances of multirotors are between 10 and 15 minutes. Theselected four-cell lithium-ion battery having a 8000 mAh capacity holds118 watts of power, providing the UAS with a theoretical 14.2 minutehover time based on power consumption during hover. However, note that alithium-ion battery can be safely discharged to only □75% of itscapacity. Under this assumption, the expected hover time is reduced tojust under 11 minutes.

The agricultural UAS is capable of VTOL and is also capable ofhorizontal flight. To achieve these capabilities, the UAS has a partialtilt-frame design, which is capable of transitioning from verticalflight to horizontal. However, the transition goes through only 45°whereas a true tilt-frame configuration goes through a pitch angledifference of 90°. Due to 45° maximum pitch during horizontal flight,the propellers are angled at 45° with respect to the incoming airflow.The propellers therefore share responsibility for generating lift withthe wings of the aircraft during horizontal flight mode. It is difficultto estimate the optimal wing area because the contribution to totallifting force of the aircraft from generated thrust is largely unknown.The ideal wing area depends on a multitude of coupled variables, such asairspeed, angle of attack, weight, drag, and thrust from motors. Usingthe estimated UAS weight, the desired wing loading, and aspect ratio(AR), wing size is calculated. Because the aircraft is capable of VTOL,the wing loading will vary with respect to aircraft pitch. Due to thepermanently 45°-rotated motors with respect to the wing, the tilt-frameUAS does not rely on wings as the single lift source in any flyingconfiguration. This makes wing loading estimations difficult because theexact fraction of lift contribution from wings is unknown. To avoidmaking an underestimate, the wing loading is calculated as if only thewings are producing lift. Note that both wing loading and aspect ratioare critical to the performance of fixed wing aircraft because manyperformance metrics are dependent on these variables. Generally, ahigher wing loading in fixed-wing aircraft increases take-off andlanding airspeeds. In contrast, higher aspect ratio for wings increasewing efficiency but tend to decrease the vehicle's airspeed. However,because the tilt-frame UAS is VTOL-capable, concerns over landing andtake-off airspeeds are not applicable. An efficient high aspect ratiowing is beneficial for endurance operations but because the agriculturalUAS lands and powers down before executing its primary missionobjective, range is more important than endurance. Note that a higherwing loading with a lower aspect ratio is desired for the agriculturalUAS to increase its cruising speed in an attempt to increase theaircraft's overall range. In particular, the maximum desired wingloading for the tilt-frame UAS is between 18 and 23 kg/m², while theaspect ratio is set to 5 for a compromise between wing efficiency andairspeed.

The overall dimensions of the UAS were calculated using the parametersand assumptions discussed above, and the needed wing span is calculatedusing the wing loading and aspect ratio parameters. The motors (andassociated PTGS hardware) were added to the tips of wings and increasedthe overall wingspan. However, the aerodynamically effective wingspanstayed constant because the added components do not contribute to winglift. The fuselage length is set to a higher value, which increases theeffective height of the VOC sensor above ground and thereby places itcloser to the tree canopy while the UAS is landed on the ground.

The physical characteristics and performance parameters for an exemplarytilt-frame agricultural UAS are summarized in Table I. Note that theweight break-down of all major components as they were installed onboardthe agricultural UAS is shown in Table I. Details behind the design,construction and implementation of these components are discussed below.

Exemplary Airframe Structure

FIG. 1A presents a perspective view of an exemplary tilt-frame unmannedaerial system (UAS) 100 in accordance with the disclosed embodiments.(FIG. 1B presents another perspective view of the tilt-frame UAS 100.)As with most aircraft, the structural material of the UAS is light andstiff. Additionally, the body and shape of the UAS is slender todecrease drag during the horizontal mode of operation. To decrease UASfrontal area, a narrow, 7.68 cm diameter cardboard tube is used as thefuselage 118. The tube is light yet rigid and is easily modified usingrelatively simple tools. The UAS main wing 104 was made from ⅜ inchthick balsa wood with the leading edge reinforced by ⅜ inch diametercarbon fiber tube. The main wing 104 is rigid, yet light, allowing forslight flexing.

As mentioned above, tilt-frame UAS 100 comprises a tri-rotor system,which includes three propellers, including: a left main propeller 102coupled to a left motor 103 in proximity to a left PTGS 124; a rightmain propeller 114 coupled to a right motor 115 in proximity to a rightPTGS 116; and a right propeller and motor 120 connected to a tail motorsupport 119.

The nose cone 108 and tail motor support 119 were 3D printed andinserted directly into the fuselage tube. (Note that nose cone 108includes an extendable boom 110, which is used to deploy a VOC samplerin proximity to a tree canopy.) Both the nose cone 108 and tail motor119 support are secured using four screws bolted through the fuselage.As Ultracote shrink-wrap film is used to cover the wings to reduce thesurface roughness and protect the balsa wood from moisture. A specialwing mounting bracket 105 was 3D printed to form a rigid connectionbetween the fuselage and wings. This wing mounting bracket 105 holdslanding gear 122 in place allowing the aircraft to maintain 45° wingpitch when resting on the ground.

Component Placement

The aircraft component placement strategy is to place the heaviestcomponents as close to the center of gravity (CG) of the aircraft aspossible. The CG of the agricultural UAS lies at ⅓ of the mean chord. Asthe largest contributor to the overall aircraft weight, the flightbattery sits inside the fuselage at a location 117, which is □4 cm awayfrom the CG. Note that the flight battery is inserted through the backof the fuselage and its position can be adjusted to achieve the desiredCG based on the payload weight for a particular mission.

Major power distribution wiring was placed inside the fuselage tominimize drag and reduce the risk of snagging on external objects. Theautopilot 112, which contains a magnetometer and an internal measurementunit (IMU), was placed on shock absorptive pads outside of the fuselagefor easy interfacing and reducing electromagnetic interference with thepower supply wires running along the inside of the fuselage. Thetelemetry radio 106, was placed as far from the autopilot 112 aspossible to reduce interference. Also, the GPS antenna 118 wasreoriented horizontal with respect to the ground instead of the fuselageto improve GPS accuracy during VTOL. The autopilot system 112 was placedas close to the CG as possible to avoid measuring erroneous motion fromaircraft structure extremities. All loose wires were wrapped in plasticwiring sheaths to increase the level of organization and reduce dragduring flight.

Propeller Thrust Governing System (PTGS)

As illustrated in FIG. 1A, tilt-frame UAS 100 is equipped with right andleft PTGS modules 116 and 124 (also called “buttery flaps”.) These PTGSmodules 116 and 124 enable tilt-frame UAS 100 to control roll and yawwithout changing the rotational velocity of its main lifting motors. Thesystem works by modulating the deflection angle of two flaps locateddirectly below the propeller. For example, FIG. 2A illustrates abutterfly flap system 200 comprising a front flap 212 and a rear flap214. Front flap 212 and rear flap 214 operate to reduce and redirect theairflow from the propeller to affect roll and yaw of the aircraft. FIG.2B presents another perspective view of butterfly flap system 200.

FIG. 2C presents a side view of butterfly flap system 200. Note that theflaps are not symmetrical about the vertical axis as shown by FIG. 2C.However, the two sets of butterfly flaps (PTGS 116 and 124) are mirroredwith respect to the fuselage on either side of the main wing 104.

FIG. 2D presents an exploded view of butterfly flap system 200 inaccordance with the disclosed embodiments. Note that the flap mechanismfor the PTGS includes a motor mount 207, which is attached to a mainmotor 208, and a wing tip mounting structure 210. Wing tip mountingstructure 210 is also attached to a main flap structure 204, which isattached to front flap 212 and rear flap 214. Front flap 212 and rearflap 214 are controlled by front flap servo 202 and rear flap servo 206,respectively. The above-listed components are combined into a singlesystem for wing tip attachment on UAS 100.

Buttery fly flap system 200 was 3D printed in five separate pieces. Notethat this 3D printing allows the system to be light and intricate indesign. Additionally, all components are held together with nylon boltssuch that upon component failure, the broken component is easilyreprinted and replaced.

Process for Gathering VOC Samples

FIG. 4 presents a flow chart illustrating the process of gatheringvolatile organic compound (VOC) samples from a tree in an orchard inaccordance with the disclosed embodiments. During operation, the systemvertically lands an unmanned aerial vehicle (UAS), which is capable ofvertical take-off and landing (VTOL), in proximity to the tree in theorchard (step 402). Next, the system shuts down a propulsion system forthe UAS to save power (step 404), and then extends a VOC sensor from theUAS toward a canopy of the tree (step 406). The system then collects aVOC sample by activating the VOC sensor for a predetermined amount oftime (step 408). After the sampling is complete, the system retracts theVOC sensor back to the UAS (step 410) and restarts the propulsion systemfor the UAS (step 412). Finally, the system performs a vertical takeoffwith the UAS (step 414), and flies the UAS back to a base or anothersampling location (step 416).

Note that in additional to collecting VOCs for agricultural purposes,the disclosed embodiments can also be used for other applications, suchas detecting leaks from remote gas lines.

Various modifications to the disclosed embodiments will be readilyapparent to those skilled in the art, and the general principles definedherein may be applied to other embodiments and applications withoutdeparting from the spirit and scope of the present invention. Thus, thepresent invention is not limited to the embodiments shown, but is to beaccorded the widest scope consistent with the principles and featuresdisclosed herein.

The foregoing descriptions of embodiments have been presented forpurposes of illustration and description only. They are not intended tobe exhaustive or to limit the present description to the formsdisclosed. Accordingly, many modifications and variations will beapparent to practitioners skilled in the art. Additionally, the abovedisclosure is not intended to limit the present description. The scopeof the present description is defined by the appended claims.

What is claimed is:
 1. An aircraft, which is capable of vertical takeoffand landing, comprising: a fuselage; a probe-deployment mechanismlocated at a front end of the fuselage, wherein the probe-deploymentmechanism is configured to deploy a sample-gathering probe; a main wingcoupled to a middle section of the fuselage; a right motor andassociated right propeller coupled to a right side of the main wing; aleft motor and associated left propeller coupled to a left side of themain wing; wherein the right and left propellers are angled with respectto the fuselage to provide thrust-generation lines, which are similarlyangled with respect to the fuselage, which enables the aircraft to pitchup to a vertical-takeoff mode and pitch down a horizontal-cruising mode;and wherein when the aircraft is pitched up, the front end of thefuselage sits higher than a rear end of the fuselage to allow theprobe-deployment mechanism to extend higher; and a pitch motor andassociated pitch propeller located at the rear end of the fuselage,wherein the pitch propeller is angled to provide substantially verticalthrust to control a pitch of the fuselage.
 2. The aircraft of claim 1,wherein the probe-deployment mechanism includes an extendable boom,which extends the sample-gathering probe away from the aircraft.
 3. Theaircraft of claim 1, wherein the sample-gathering probe is configured tosample volatile organic compounds (VOCs).
 4. The aircraft of claim 1,wherein the aircraft further comprises one or more landing supports,which support the aircraft after a vertical landing so that the frontend of the fuselage sits higher than the rear end of the fuselage, whichfacilitates extending the sample-gathering probe above and away from theaircraft.
 5. The aircraft of 4, wherein the one or more landing supportsinclude the following three landing supports: a right leg extending fromthe middle section of the fuselage; a left leg extending from the middlesection of the fuselage; and a tail support extending from the rear endof the fuselage.
 6. The aircraft of claim 1, further comprising: a rightpropeller-thrust-governing system (PTGS) located in proximity to theright propeller; and a left PTGS located in proximity to the leftpropeller; wherein the right and left PTGSs are adjustable to reduceand/or redirect thrust from the associated right and left propellers. 7.The aircraft of claim 6, wherein by reducing and/or redirecting thrustfrom the left and right propellers, the left and right PTGSs control aroll-axis rotation and a yaw-axis rotation for the aircraft.
 8. Theaircraft of claim 6, wherein each PTGS comprises a pair of adjustablebutterfly flaps located in an airflow of an associated propeller.
 9. Theaircraft of claim 7, wherein each pair of butterfly flaps includes: afront-facing flap, which faces a front of the aircraft; and arear-facing flap, which faces a rear of the aircraft.
 10. The aircraftof claim 1, wherein the left motor, the right motor and the pitch motorcomprise a tri-motor system, wherein the left and right motors areprimarily responsible for generating thrust and controlling roll-axisand yaw-axis rotations for the aircraft, and wherein the pitch motor isprimarily responsible for controlling a pitch-axis rotation for theaircraft.
 11. The aircraft of claim 1, wherein the right and leftpropellers are fixedly attached to the main wing so that the angles ofthe right and left propellers cannot change with respect to thefuselage.
 12. The aircraft of claim 1, wherein the pitch motor comprisesa variable-speed motor.
 13. The aircraft of claim 1, wherein theaircraft comprises an unmanned aerial vehicle (UAV).
 14. Apropeller-thrust-governing system (PTGS) for an associated propeller,comprising: one or more a control surfaces located in an airflow of theassociated propeller; wherein the one or more control surfaces areadjustable to reduce a thrust produced by the associated propeller; andwherein the one or more control surfaces are also adjustable to redirectthe thrust produced by the associated propeller.
 15. The PTGS of claim14, wherein the PTGS and the associated propeller are components of anaircraft; and wherein by reducing and/or redirecting the thrust producedby the associated propeller, the PTGS facilitates controlling one ormore of the following for the aircraft: a roll-axis rotation; a yaw-axisrotation; a pitch-axis rotation; and a level of propulsion.
 16. The PTGSof claim 15, wherein the one or more control surfaces comprise a pair ofadjustable butterfly flaps located in the airflow of the associatedpropeller.
 17. The PTGS of claim 16, wherein each flap in the pair ofadjustable butterfly flaps is independently controllable.
 18. The PTGSof claim 16, wherein the pair of adjustable butterfly flaps includes: afront-facing flap, which faces a front end of the aircraft; and arear-facing flap, which faces a rear end of the aircraft.
 19. The PTGSof claim 17, wherein the pair of adjustable butterfly flaps includes: astandard flap in a standard orientation, wherein a hinged leading edgeof the flap is closer to the associated propeller than a trailing edgeof the flap; and an inverted flap in an inverted orientation, whereinthe trailing edge of the flap is closer to the associated propeller thanthe hinged leading edge of the flap.
 20. A method for gathering volatileorganic compound (VOC) samples from a tree in an orchard, comprising:vertically landing an unmanned aerial system (UAS), which is capable ofvertical take-off and landing (VTOL), in proximity to the tree in theorchard; shutting down a propulsion system for the UAS; extending a VOCsensor from the UAS toward a canopy of the tree; collecting a VOC sampleby activating the VOC sensor for a predetermined amount of time;retracting the VOC sensor back to the UAS; restarting the propulsionsystem for the UAS; performing a vertical takeoff with the UAS; andflying the UAS back to a base or another sampling location.